<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8" />
  <meta name="viewport" content="width=device-width, initial-scale=1.0" />
  <title>Document</title>
  <script src="../js/vue.js"></script>
</head>

<body>
  <div id="root">
    <h2 v-if="a">hello</h2>
    <h2 :style="{opacity}">no to be</h2>
  </div>

  <script>
    const vm = new Vue({
      el: '#root',
      data: {
        a: false,
        opacity: 1,
      },
      methods: {},
      // 完成模板的解析并把初始的真实DOM元素放入页面后(挂载完毕)调用mounted
      mounted() {
        console.log('mounted', this);
        setInterval(() => {
          this.opacity -= 0.01;
          if (this.opacity <= 0) this.opacity = 1;
        }, 16);
      },
    });

    //   // 不推荐
    //   setInterval(() => {
    //     vm.opacity -= 0.01;
    //     if (vm.opacity <= 0) vm.opacity = 1;
    //   });
  </script>
</body>

</html>